Hopkins and colleagues from Emergent BioSolutions identify several issues with our model for responding to a small scale anthrax attack.1 They are concerned that our model of preattack vaccination denied unvaccinated workers postattack antibiotics, that we underestimated vaccine efficacy, and that our 10-year time horizon was inadequate. They argue that these deficits produced an erroneous effectiveness assessment of preattack vaccination. Furthermore, they suggest we overestimated vaccine administration cost and excluded costs of cleanup and work force displacement inflating total cost of a preattack vaccination strategy. Lastly, they were concerned we had not stratified exposure risk among workers within the USPS.